LONELINESS is as big a killer as obesity and as dangerous to health as smoking 15 cigarettes a day, according to a study of three million people.

The research studied three million people and found loneliness is a killer

While the elderly are more likely to live alone, younger adults are likelier to have their life expectancy cut due to growing isolation, the researchers said.

Loneliness is defined as living alone and social isolation as being lonely even when “surrounded by lots of people” said the study conducted at Brigham Young University in Utah, USA.

Researchers analysed data on adult lifestyles and health from a host of other studies covering a total of three million adults aged 65 or under.

They found the link between loneliness and a premature death was as great as that of obesity while the effect on health was the equivalent of being an alcoholic or smoking 15 cigarettes a day.

Lead author Julianne Holt-Lunstand warned: “We need to start taking our social relationships more seriously. The effect of this is comparable to obesity, something that public health takes very seriously.

“A growing proportion of people across the world are now living alone and at greater risk of isolation.”

The study, published in the journal Perspectives On Psychological Science, said an ageing population was an obvious cause but so were higher divorce rates and people willing to move home to find work elsewhere.

While being connected online can help overcome some feelings of isolation, that contact needs to be more than superficial emails or texting, it said.

Online experiences should include “emotional context and depth”.

Warning of a “loneliness epidemic” in the future, coauthor Tim Smith added: “The more positive psychology we have in our world, the better we’re able to function not just emotionally but physically.”